Total knee replacement (“TKR”) is a commonly-used procedure for correcting deformities and repairing damage to the knee joint. The procedure used for TKR is generally known in the art and includes many variations. Generally, such a procedure includes exposing the knee joint by forming at least one incision through the soft tissue in the knee area and retracting the wound. The joint is then resected, which includes removing the damaged portions of the joint. This typically includes removing one or both of the femoral condyles and/or the tibial plateau, which is typically accomplished by forming a series of cuts according to any one of various patterns. The cuts are typically made so that the bone can accept an artificial replacement for the resected portions of the joint. As the precise anatomy of the knee on which TKR is preformed varies significantly among patients, it is necessary to provide artificial replacements for the knee components in various shapes and sizes. It is also necessary to form the cuts in the bones of the knee joint to appropriately accept the implant that best suites the anatomy of the individual joint as best suited for the patient.
In order to facilitate the appropriate joint resection and artificial joint selection, various trial implants have been developed are used in “trial reduction” of the resected joint. To assist in trial reductions, a number of differently sized “trial” joint implants (which are also referred to as “provisional” implants) are supplied. After a preliminary estimate of the appropriately sized implant is made, trial implants are inserted into the resected joint, usually on both the femur and on the tibia. The implant is then examined for proper fit, and the joint is tested for proper kinematics. If the fit of the trial is improper, different trials are selected in succession until proper fit is achieved. Selection of differently sized trials may require further joint resection. Once a proper size determination has been made, a permanent joint implant of a size which corresponds to that of the appropriately-sized trial is affixed within the joint. In TKR this typically includes affixing permanent implants into both the femoral and the tibial components of the knee. A similar trial reduction procedure is used to determine proper implant fit in a total hip replacement (THR) procedure.
Trial femoral components must accurately match the geometry of the permanent implant to be used in TKR. Further, femoral trials must be sufficiently rigid to replicate proper joint kinematics. Costs associated with manufacturing such trial components has lead to known trial components being made so as to be reusable throughout multiple procedures. Reuse of trials requires that the trials be sterilized prior to each use, which is typically done using an autoclave procedure. Such a procedure is somewhat rigorous with respect to the items subjected thereto, which further requires robust construction of the trials. In response to these requirements, known trial components have been manufactured from cast cobalt-chromium (CoCr) or stainless steel (“SS”), both of which can withstand multiple autoclave cycles and are sufficiently rigid to provide accurate trial reduction. However, the processing required to impart the necessary geometry onto these materials requires many secondary operations, such as CNC grinding or polishing. The material properties of CoCr and of SS are such that these secondary operations require relatively low feed and tool speed rates to properly create the complex geometries that are part of the trial. Each of these secondary operations is, thus, costly and time consuming, leading to a large overall cost increase of trial components.
In addition to the cost associated with processing the cast materials of typical trials, the density of the material can be quite high, resulting in a relatively heavy component. Each trial component may weigh approximately 1-1.5 pounds, a weight which becomes problematic due to the methods employed during TKR and THR procedures. Currently, validated sterilization methods require each component that may potentially enter the sterile field to be steam-sterilized prior to surgery (typically via an autoclave process) As a result, all surgical tools that may potentially be used during TKR and THR procedures are kitted and held in sterilization trays. The kitting of instruments is based on the surgical steps for which they are required as part of a particular procedure. As a result, all instruments required to complete a step are preferably stored in one tray or case. Multiple trays are then placed into a sterilization case and the case is processed through the sterilization process and brought into the operating room. In the case of femoral trials, because final determination of femoral size is made interoperatively, all such devices for a given TKR system are housed on a single tray and brought into the operating room together. A typical TKR system can have eight differently sized trials for both the left and right femoral components, resulting in sixteen femoral trials being stored in a single sterilization tray. Based on the average trial weight, the fully-loaded tray may twenty pounds or more. When combined with the other trays contained in the sterilization case, total case weight is significant. The same problem applies for THR procedures: as with femoral sizing, proximal stem sizing must be performed interoperatively. Therefore, a fully-loaded THR tray may also weigh upwards of twenty pounds.
It is therefore desired to provide a trial component that has a reduced weight, and which reduces costly process steps, while retaining the desired characteristics for such a component.
As used herein when referring to bones or other parts of the body, the term “proximal” means close to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means toward the head. The term “anterior” means toward the front part or the face and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body.